Semiconductor switching devices are powerful and fast turnoff components having a cathode-anode-gate structure. Specifically, the semiconductor switching device comprises a substrate having deposited thereon a cathode, an anode, and a gate of the switching device. The device further comprises connection means for electrically connecting the cathode, the anode and the gate of the switching device to an external circuit unit.
A semiconductor switching device has to handle large currents and voltages. One example of such a semiconductor switching device is an integrated gate commutated thyristor (IGCT). An IGCT is a gate-controlled turn-off switch which turns off like an insulated gate bipolar transistor (IGBT), but conducts like a thyristor with the lowest conductor losses. An integrated gate commutated thyristor is a power switching device for demanding high power applications such as, e.g. medium voltage drives, traction, wind power converters, AC excitation systems, battery energy storage systems, solid state breakers, traction line boosters, traction power compensators and induction heating.
A semiconductor switching device constructed as an IGCT nowadays is used in a variety of applications due to its versatility, efficiency and cost effectiveness. A conventional IGCT device has a ring-shaped structure where on a cathode disc a gate disc is arranged providing a gate connection to the switching device. An anode phase is arranged on top of a housing having for instance a specific creepage distance at the outside.
For operation of an IGCT for instance a maximum turn-off current has to be commutated via a gate-cathode connection to a gate unit during turn-off. The maximal allowable time interval for current commutation is given by the vertical and segment structure of the device and in principle it does not scale with the size of a wafer the device is formed on. However, the desired maximum turn off current depends strongly on said size of the wafer and is significantly reduced with increasing size. Thus, with the need of larger devices for high power applications there is also the need to increase the maximum turn off current.
In order to achieve a high turn off current a gate voltage may be increased. However, with increasing the voltage additional losses at the gate unit occur. Thus, increasing the gate voltage is not feasible in most circumstances. At a given gate voltage, however, the maximum turn off current is inversely proportional to a gate circuit impedance or in other words the lower the gate circuit impedance is the higher is the achievable maximum turn off current. Thus, reducing the impedance is one way to achieve higher maximum turn off currents.
In addition, it is important to be able to mount the semiconductor switching device easily in the housing. Furthermore, proper alignment and support of all parts inside a housing is important to guarantee proper contacting even after transport.
EP 1 220 314 A2 shows a prior art pressure contact for a thyristor module. Two ring pieces surrounding the thyristor latch in each other by having protrusions and recesses. To the lateral sides, the ring system is insulated by an insulation element. On the top side, an electrical main connector leads upwards. Each thyristor element is fixed to the base plate by screws arranged around each ring system. To the bottom side, a plurality of such thyristors are separately insulated from a base plate. The thyristors are arranged laterally from each, electrically connected to each other by a common main electrode plate, i.e. no compact arrangement is possible and the thyristors cannot be arranged in stack configuration. As all thyristors have to be directly mounted on the common base plate together, no modular design is possible.
EP 0 687 014 A2 shows a single light trigger thyristor element, which is pressed with its main electrodes to a substrate by a centrally arranged spring, which spring also presses a light guide to a central portion of the thyristor.
U.S. Pat. No. 3,280,389 A shows a rectifier stack, in which a spring is inserted between two pressure pieces, all of which are fully integrated in the main electrode path of the stack. The thyristors in the stack are pressed in their central part.